Betrothal and marriage

Tion had been betrothed to a daughter of Lord Rowan. However, after his twin brother Tywald died, Tywald's betrothed, Ellyn Reyne, convinced him to espouse her instead. While Lord Gerold opposed the match, in the end, he gave way, and Tion and Ellyn became betrothed.[2] According to semi-canon sources, Lord Gerold agreed to the match when Tion told his father how Tywald, with his last words, had pleaded with Tion to “take care of Lady Ellyn”.[5]
In 235 AC, Tion and Ellyn were married at Casterly Rock. In the same ceremony, Tion's younger brother Tytos was married to Lady Jeyne Marbrand.[2]

Tion's widow, Ellyn, had been quite influential as the future Lady of Casterly Rock, but with Tytos Lannister now the heir to Lord Gerold's seat, Ellyn's power dwindled.[2] According to semi-canon sources, Lady Ellyn made one final attempt to cling to her place. She declared that she was pregnant with Tion's child. However, months went by and her belly remained flat, proving her words untrue.[5]